MILLIONS OF FISH have washed up dead in south-eastern Australia in a die-off that authorities and scientists say is caused by floods and hot weather.

The Department of Primary Industries in New South Wales said the fish deaths coincided with a heatwave that put stress on a system that has experienced extreme conditions from wide-scale flooding.

The deaths were likely caused by low oxygen levels as floods receded, a situation made worse by fish needing more oxygen because of the warmer weather, the department said.

Residents of the Outback town of Menindee complained about the impact of the dead fish.

Jan Dening said: “We’ve just sort of started to clean up, and then this has happened, and… you’re walking around in a dried-up mess and then you’re smelling this putrid smell. It’s a terrible smell and horrible to see all those dead fish.”

Nature photographer Geoff Looney found huge clusters of dead fish near the main weir in Menindee on Thursday evening.

“The stink was terrible,” he said. “I nearly had to put a mask on. I was worried about my own health.

“That water right in the top comes down to our pumping station for the town. People north of Menindee say there’s cod and perch floating down the river everywhere.”

Mass kills have been reported on the Darling-Baaka River in recent weeks. Tens of thousands of fish were found at the same spot in late February, while there have been several reports of dead fish downstream towards Pooncarie, near the borders of South Australia and Victoria states.

Enormous fish kills occurred on the river at Menindee during severe drought conditions in late 2018 and early 2019, with locals estimating millions of deaths.